The present invention relates to a voltage detection circuit for storage devices, and particularly relates to a voltage detection circuit for detecting abnormality of respective terminal-to-terminal voltages of a plurality of storage devices connected in series.
A configuration in which a plurality of storage devices are connected in series to obtain a high voltage is used in batteries for electric automobiles, forklifts and the like by way of example.
In such a battery in which a plurality of storage devices have been connected in series, abnormality of voltage may be caused by a failure of the storage devices, consumption thereof, or the like, so as to damage the performance of the battery.
It is therefore necessary to provide a voltage detection circuit for the storage devices. This voltage detection circuit for the storage devices monitors the voltages of the respective storage devices, and outputs a detection signal designating the abnormality of voltage when any one of the monitored voltages is out of its specified value.
A related-art example of such a voltage detection circuit for storage devices will be described below with reference to FIG. 2. FIG. 2 is a circuit diagram showing a related-art voltage detection circuit.
In FIG. 2, the reference signs B1 to B4 represent storage devices; Q1 to Q4, semiconductor switching devices; q1 to q4, control signal generating transistors; Vp1 to Vp4, voltage judgment units; and PH0 to PH4, photo-couplers.
In FIG. 2, the storage devices B1 to B4 are connected in series, and the voltage detection units Vp1 to Vp4 are connected between terminals of the storage devices respectively.
In addition, the semiconductor switching devices Q1 to Q4 are connected between the storage devices B1 to B4 and the voltage judgment units respectively.
The base of the semiconductor switching device (e.g. transistor or FET) Q1 which is a control terminal is connected to be supplied with the output of the photo-coupler PH0 which is switched ON/OFF in accordance with an external control signal c.
On the other hand, the base of another semiconductor switching device Q2 which is a control terminal is connected to the collector of the control signal generating transistor q1 through a resistor.
The base of the control signal generating transistor q1 is voltage-divided by resistors and connected to the opposite ends of the voltage judgment unit Vp1 on the output side of the semiconductor switching device Q1.
In addition, the base of another semiconductor switching device Q3 which is a control terminal is connected to the collector of the control signal generating transistor q2 through a resistor.
The base of the control signal generating transistor q2 is voltage-divided by resistors and connected to the opposite ends of the voltage judgment unit Vp2 on the output side of the semiconductor switching device Q2.
Further, the base of further another semiconductor switching device Q4 which is a control terminal is connected to the collector of the control signal generating transistor q3 through a resistor.
The base of the control signal generating transistor q3 is voltage-divided by resistors and connected to the opposite ends of the voltage judgment unit Vp3 on the output side of the semiconductor switching device Q3.
Further, a terminal is led out from the collector of the control signal generating transistor q4 so as to connect the collector with a not-shown next-stage semiconductor switching device.
In addition, the base of the control signal generating transistor q4 is voltage-divided by resistors and connected to the opposite ends of the voltage judgment unit Vp4 on the output side of the semiconductor switching device Q4.
Judgment outputs (e.g. not lower than a predetermined voltage or not high than a predetermined voltage) from the voltage judgment units are extracted and supplied through the photo-couplers PH1 to PH4 respectively while being electrically isolated from one another.
In FIG. 2, the outputs of the photo-couplers PH1 to PH4 are connected in parallel so that an output a is supplied when any one of the terminal-to-terminal voltages of the storage devices B1 to B4 is not higher than the predetermined voltage or not lower than the predetermined voltage by way of example.
Next, the operation of the voltage detection circuit will be described in the circuit of FIG. 2.
When the output of the photo-coupler PH0 is supplied to the base of the semiconductor switching device Q1 in accordance with the external control signal c, a current flows from the emitter to the base in this semiconductor switching device Q1 so that the semiconductor switching device Q1 is turned ON.
When the semiconductor switching device Q1 is turned ON, a current from the collector of the semiconductor switching device Q1 flows from the base to the emitter in the control signal generating transistor q1 so that the control signal generating transistor q1 is turned ON.
Then, when the control signal generating transistor q1 is turned ON, a current flows from the emitter to the base in the semiconductor switching device Q2 so that the semiconductor switching device Q2 is turned ON.
Further, when the semiconductor switching device Q2 is turned ON, a current from the collector of the semiconductor switching device Q2 flows from the base to the emitter in the control signal generating transistor q2 so that the control signal generating transistor q2 is turned ON.
Then, when the control signal generating transistor q2 is turned ON, a current flows from the emitter to the base in the semiconductor switching device Q3 so that the semiconductor switching device Q3 is turned ON.
Further, when the semiconductor switching device Q3 is turned ON, a current from the collector of the semiconductor switching device Q3 flows from the base to the emitter in the control signal generating transistor q3 so that the control signal generating transistor q3 is turned ON.
Then, when the control signal generating transistor q3 is turned ON, a current flows from the emitter to the base in the semiconductor switching device Q4 so that the semiconductor switching device Q4 is turned ON.
On the contrary, when the external control signal c is absent, no current flows from the emitter to the base in the semiconductor switching device Q1. Therefore, the semiconductor switching device Q1 is turned OFF.
When the semiconductor switching device Q1 is turned OFF, the respective control signal generating transistors q1 to q4 are prevented from being turned ON. Thus, all the semiconductor switching devices Q1 to Q4 are OFF.
As described above, all the semiconductor switching devices Q1 to Q4 can be turned ON/OFF in accordance with the single external control signal c. Thus, the voltages of the storage devices B1 to B4 can be detected (judged) in the following manner by the voltage judgment units Vp1 to Vp4 connected through those semiconductor switching devices.
In FIG. 2, assume that the voltage judgment units VP1 to VP4 supply detection outputs to the photo-couplers PH1 to PH4 when input voltages to the voltage judgment units VP1 to VP4 are not higher than a predetermined voltage. In this case, if the output a is obtained when the external control signal c is present, it can be concluded that any one of the terminal-to-terminal voltages of the storage devices B1 to B4 is not higher than the predetermined voltage, or constituent parts of this circuit are abnormal.
On the contrary, assume that the voltage judgment units VP1 to VP4 supply detection outputs to the photo-couplers PH1 to PH4 when input voltages to the voltage judgment units VP1 to VP4 are not lower than a predetermined voltage. In this case, if the output a is obtained when the external control signal c is present, it can be concluded that any one of the terminal-to-terminal voltages of the storage devices B1 to B4 is not lower than the predetermined voltage, or constituent parts of this circuit are abnormal.
On the other hand, if the output a is obtained when the external control signal c is absent, it can be concluded that constituent parts of this circuit are abnormal.
In the circuit of FIG. 2, such detection mechanisms are combined so that the abnormality of the terminal-to-terminal voltages of the storage devices B1 to B4 and the abnormality of the constituent parts of this circuit can be judged.
In the circuit of FIG. 2, the abnormality of the terminal-to-terminal voltages of the storage devices B1 to B4 and the abnormality of the constituent parts of the circuit can be indeed judged, but a large number of photo-couplers PH1 to PH4 for electric isolation are required to extract the detection outputs of the respective voltage judgment units to the outside. Thus, there is a problem that the cost increases.